Fluorinated carboxylic acids have been used as synthetic intermediates in the preparation of industrial and specialty chemicals and as emulsifiers or dispersants in the preparation of polymers (e.g., polymerization of fluorinated monomers). In the past perfluorinated low molecular carboxylic acids of the general formula CF3-(CF2)n-COO— M+ have been used for the polymerization of fluorinated monomers, wherein M+ represents a cation and n represents an integer between 4 and 8. However, alternative fluorinated emulsifiers have become of interest for various reasons. Fluorinated polyether carboxylic acids and partially fluorinated carboxylic acids have been suggested as alternative emulsifiers. In particular the fluorinated carboxylic acids described in U.S. Publ. No. 2007/0015865 (Hintzer, et al.) and U.S. Pat. No. 7,671,112 (Hintzer, et al.). For example, the highly fluorinated fluoroalkoxy carboxylic acids of the general formula [Rf—O—L—COO—]iXi+, wherein L represents a linear partially or fully fluorinated alkylene group or an aliphatic hydrocarbon group, Rf represents a linear partially or fully fluorinated aliphatic group interrupted with one or more oxygen atoms, Xi+ represents a cation having the valence i and i is 1, 2 or 3 (as described in U.S. Pat. No. 7,671,112) have been found to be useful alternatives.
Various methods have been described to prepare fluorinated carboxylic acids. For example, (U.S. Pat. No. 7,589,234 to Morita et al.) describes a process based on a ring opening reaction of tetrafluorooxetanes to create acid fluorides which are then converted into carboxylic acids. However, this process is cumbersome and involves various reaction steps. Additional methods describe preparing fluorinated carboxylic acids from the corresponding fluorinated alcohols. Such methods include the use of strong oxidizing agents as disclosed in U.S. Pat. No. 7,671,112 to Hintzer et al. and include for example, potassium permanganate (Dmowski, et al., J. Fluor. Chem., 1990, v. 48, 77-84), potassium dichromate/sulfuric acid (Hudlicky et al., J. Fluor. Chem., 1992, v. 59, 9-14), pyridinium dichromate, chromium (VI) oxide with sulfuric acid, RuO4 or OsO4, and nitric acid, and some lesser known methods such as irradiation in the presence of chlorine gas. While these reactions may be carried out in an industrial scale with good yields, these methods are undesirable on large scales due to concerns with, among other things, heavy metal disposal, low yields, high temperatures, and the use of expensive reagents. Therefore, there is the need for an alternative process for making fluorinated carboxylic acids.